1. Field of the Invention
The invention relates to solvent-free or low-solvent two-component polyurethane coating compounds based on combinations of certain polyisocyanates and certain polyhydroxyl compounds and their use for the manufacture of floor sealers and floor coatings.
2. Description of the Prior Art
Floor sealers are coatings with a dry film thickness between 60 and 250 .mu.m, which are applied to floors for the purpose of solidifying the substrate, providing an aesthetically pleasing finish and increasing the chemical resistance, wear resistance and scratch resistance. For example, floor sealers are used to solidify cement floors and render them scratch-resistant. If no particular requirements are set for crack-bridging capability, they are also used to provide cement floors, which are susceptible to yellowing, with an aesthetically more pleasing and more color-constant covering layer. Further, they are used to renovate old, heavily scratched and damaged floor coatings without having to provide a completely new coating.
A range of well-tried polyurethane systems are available to the custom molder for floor sealers. The sealers previously used were one-component systems based on NCO prepolymers of 4,4'-diisocyanato-diphenyl methane (cf. e.g. the Technical Memorandum of the Applicant "Desmodur E 21" of December 1990). However, these systems have a tendency to subsequently turn yellow, and generally must be mixed with volatile solvents for their application. Other known sealers include those based on NCO prepolymers of 1-isocyanato-3,3,5-trimethyl-5-isocyanato-methylcyclohexane (IPDI) and oxazolane resins as introduced by K.-H Hentschel and E. Ju/ rgens at the XXI. FATIPEC-Congress (1992) in Amsterdam (cf. Congress Bulletin, Vol 3, pp 87 et seq.) and those based on combinations from urethanized toluene diisocyanate and polyester polyols (cf. e.g. Technical Memorandum of the Applicant "Desmodur L", 1.1.86 edition). However, these sealers also require substantial quantities of volatile solvents for their application.
In view of their excellent color consistency, combinations of polyisocyanates containing biuret or isocyanurate groups based on hexane 1,6-diisocyanate with polyester polyols are also widely used for providing a decorative finish to plastic floor coatings (cf. e.g. the paper given by W. Kubitza at the International Symposium on Industrial Floorings from 15.1 .to 17.1.91, Bulletin, pp. 533-537).
Such floor sealer s may be applied fully solvent-free and harden to form films which are very easily cleaned. However, only a moderate wear and scratch-resistance may be achieved, as such sealer. s are relatively soft. Sealers with substantially better hardness and wear resistance properties are based on combinations of the above-mentioned HDI-based polyisocyanates with hydroxy-functional polyacrylate or polymethacrylate resins. However, this advantage is offset by their high solvent content.
Therefore, an object of the present invention is to provide polyurethane-based coating compositions, which are suitable, in particular, for sealing floor surfaces, may be formulated to be solvent-free or low solvent-containing, fully harden rapidly under a wide range of ambient conditions and produce easy-to-clean sealing films with good chemical resistance and provide good color stability, a high degree of hardness and excellent scratch and wear resistance.
This object may be achieved with the two-component polyurethane coating compositions according to the invention, which will be described in further detail below. The coating compositions according to the invention may be processed solvent-free or with low solvent content. These systems have a content of solvents inert to isocyanate groups with a boiling point below 180.degree. C. at normal pressure of less than 20, preferably less than 10 wt. %. In particular, the coating compositions according to the invention do not contain such readily volatile solvents.